1. Field of the Invention
The invention relates to a safety device arranged on the movable excavation devices of an underground mine.
2. Description of Related Art
Such a personnel protection system is employed in underground mining operations in the areas proximate to all moving machines and machine components, for example planes, shearers, loading machines, conveyors, conveyor vehicles, and similar machines. The safety area associated with these personnel protection systems should correspond as precisely as possible to the area affected by the machines, in order to avoid superfluous work halts.
This is especially important for shield mining in a longwall mine, because the number of support shields along a longwall can range from 100 to 300 units; for this reason, on the one hand, comprehensive personnel protection is difficult, and on the other hand, losses resulting from unnecessary stoppages and the associated disruptions of operations are high. Shields are included in the definition of the term “support shields” in this description, or more generally as excavation devices. This description of the invention relates primarily to applications in longwall coal mining and to the support shields/chocks utilized therein.
As in the case of many other excavation devices those support shields in a longwall mine are moved automatically or by remote control, depending on the position and direction of movement of the mining machine. Particularly in the case of automatic processes, visual and acoustic warning signals are given. Nevertheless, a risk still exists, particularly for persons who are unexpectedly incapable of moving, or for any other reason cannot reach the emergency shutoff switch.
For the protection of all personnel in a longwall mine, it is possible to monitor their current location. With the provision of current locations for personnel, the excavation devices which pose a danger for those persons can be blocked manually or automatically by electronic control. For the purpose of detecting the current location of each person present in the longwall mine, each person is equipped with an element which is detected by a “reading device” associated to each excavation device. The presence of the element and person is then signaled to excavation device controller (device controller unit, particularly support shield controller unit) or the central control (longwall controller unit).
There are two possibilities for the technical implementation of this approach:                i. Each person in the longwall mine carries a passive element, for example a coil or a passive transponder. In each excavation device/support shield, an active transmitter/receiver element is installed, which detects this passive element.        
or                i. Each person in the longwall mine is equipped with an active transmitter/receiver element which is normally in standby mode (sleep mode). An element attached to each excavation device, e.g. support shield, initially activates the transmitter/receiver worn by the person, at which point said transmitter/receiver is detected and identified by means of its signals.        
Such safety devices are known for support shields (chocks) from DE10029918A1 and the prior art referenced therein. In that case, the device is intended to ensure that no person is located in the area of motion in which the machine travels when the support shield is in motion. For this purpose, the area of motion is scanned by sensors which are simultaneously activated by the control unit for the support shield upon every movement of the same.
Even with this method, safety cannot be ensured in a comprehensive manner. These sensors (DE10029918A1) arranged on the support shields execute self tests at regular or irregular intervals. However it cannot be ruled out that the passive element (coil or passive transponder), or the active transmitter/receiver element which must be worn by each person, is defective or is failing for another reason to function correctly, or the safety areas of the excavation devices do not fully extend to cover all possible personnel locations. This can occur particularly in the case of coal seams with larger thicknesses.
The problem addressed by the invention is that of removing these gaps in the area of protection.